Method for the deoxidation of technically pure zinc



F. "SCHREIBER 2,121,306 METHOD FOR THE DEOXIDA'I'ION OF TECHNICALTJY PURE ZINC June 21, 1938.

Filed Aug. 15, 1934 llllllllllllllllllll'lr qvVENmR: i Z ,i-hrezber RNEYS.

20 With iron, it is similarly so.

Patented June 21, 1938 UNITED STATES PATENT OFFICE METHOD FOR THE nEoxmArro on TEOHNICALLY runs zmo Franz Schreiber, ologne-Kl'ettenberg, Ger

' many 4 Claimsh (Cl. Ja s-8s) Technically obtained zinc cannot, metal-- lographically, be regarded-as a unitary system, but its character is, according to my opinion,

that of a metal compound. The process of mak-- ing it in the zinc muflles suggests the assumption that the contaminating metals occurring in the ores or of which small amounts find access into the final products, via, the virgin zinc obtained by smelting zinc ores are able toform a binary 10 system with the zinc, I mention, in. the first place, cadmium. This metal evaporates from the ores at a lower temperature than the zinc but this difference of temperature is not sufii-.

ciently great to render an accurate separation possible, as, even if the cadmium vapor is withdrawn preliminarily while the ores are being roasted, still, there presents itself an opportunity for said vapor to get admixed to the zinc vapor, because technical zinc always contains cadmium.

zinc form, according to my opinion a binary alloy while the zinc is being made.

Under ternary alloys I understand an; alloy having three components, in the present case, zinc, iron and oxygen; by a quaternary alloy I V understand correspondingly a combination of four components, e. g. between iron, zinc, and iron-oxygen and zinc-oxygen compounds.

I have repeatedly investigated the system of compounds of iron and zinc which arise in the treatment of virgin zinc during its reduction and believe that it is not a binary iron-zinc system but either a ternary system, or, if the zinc as well as the iron can form several chem? cal compounds with oxygen even a quaternary system},

I entertain also the opinion that cases of the above-mentioned kind can arise already while the manufacturing process is being carried out, thatis to say, that mixed crystals of such ternary or quaternary alloys are contained already in the virgin zinc obtained by smelting zinc ores.

The components or groups of components of the virgin zinc obtained by smelting zinc ores must be divided, according to my opinion, into three groups, viz.

(at) Pure zinc,

(b) Elements of metallic kind,- such as iron, cadmium, etc, and, V

(c) Gases, first-of all oxygen.

These components become introduced into said virgin zinc already while the zinc ores are being smeltedytheir influence upon the behavior of the zinc is very considerable. This can be scientifically proven by the changes of the curves of state showing the time, the temperature, and

This metal and the expansion relationship of the zinc containing the groups of-substances described under 2; and c which substances are contained in smelted zinc and change the trend of the curve as compared with the curve of state obtained in the fusion of. 5

pure zinc, and also practically by the z changes of thevi'scosity, the limit of expansion'and the limit of stretching, and finally and chiefly by the diffusion tendency and diffusion speed relatively to metals other than zinc. As regards the notion diffusion in general I comprehend thereunder the phenomenon that different solid or liquid or molten or g'asiform substances intermix by themselves, without being subjected to anyv exterior influence. As regards the notion dif- 5 fusion tendency I comprehend thereunder the degree or strength of the attraction which causes the respective different substances to intermix by themselves without being subjected to any ex-- terior influence. And as regards thenotion diffusion speed Icomprehend thereunder the speed with which the respective substances intermix by themselves without being subjected to any exterior influence.

Starting from this assumption the knowledge of the equilibrium diagram of the most important compounds of the-zinc with other elements of binary or tertiary kind is, of course, extremely important for a successful application of the invention to the virgin zinc obtained by smelting 30 zinc ores in the state in which it is delivered from the smelting works for the manufacture oi zinc coatings.

The direct proof for the existence of a ternary or quaternary alloy in contradistinction to the 35 seemingly existent only binary alloy can be given only with difficulty, the difliculty being to find methods which render visible the crystalline form of said alloys. But I think-that various investigations which I have carried out and 4 which have given conformable results constitute a reliable proof of their existence, and these results constitute the basis for the present invention for the deoxidation of zinc.

Diffusion can take place between solid substances, as well as between solid and liquid substances and also between solid or liquid and gasiform substances. Now, concerning the present invention, a particularlyimportant part for'the success thereof is played by that ternary eutectic 50 which contains, besides zinc, also an oxygen compound or oxygen compounds.

It is, as will be more fully dealt with. hereinafter, particularly striking that the diffusion speed between the zinc and the oxygen may be W greatly changed. When the oxygen has been completely removed from the molten zinc, this latter can according to my opinion take up another amount of oxygen only from the air. If only a part of the oxygen has been removed, the other part remains, of course, in the molten zinc this oxygen forming so-to-say oxidizing foci which produce a further oxidation of the zinc and a quick re-oxidation of the same at the open air. If, on the other hand, the zinc is entirely free from oxygen, it lacks according to my opinion the requisite tendency to take up quickly a fresh amount of oxygen.

The improved method is carried out within a range of temperature determined by a cooling curve described below. The zinc, heated to the condition it assumes within said range of temperature and metals that have a higher fusing point than zinc and a very good aifinity for oxygen are brought into the most intimate possible contact by relative motion therebetween, treated in said manner preferably during an interval of temperature indicated by two points of discontinuity in the course of a curve, which can, as will hereinafter be shown with the aid of a figure, be determined, on the one hand, by the degrees of heat given off by the molten zinc as this is being transformed into solid state by cooling, and on the other hand by the degrees of heat to be taken up by the cooled zinc as it is to be re-transformed into liquid state. That time-temperature-curve has in its course a point of discontinuity at which the .congealing commences and a point at which the liquefaction commences; both points exist always, irrespective ,of whether the transformation from the liquid state into the solid one or from the solid state into the liquid one is just taking place.

This means that the perfect liquefaction can take place only at a heat content which is sub-' stantially greater than can be ascertained by a mere observation of the metal concerned, and that it can be ascertained only by tracing the above-mentioned curve. The positionof said two points of discontinuity depends upon the composition of the material with respect to its contents of metal and of metal oxides. The particular treatment is to be carried out always within the limits indicated by the said two points of discontinuity.

If, when a quantity of metal is being heated,

the lengths of the periods of time are traced graphically in an ordinate system ABD as abscissae, and the temperatures are traced as "ordinates, one can often perceive that near the liquefaction limit the temperature does not rise uniformly, but remains nearly the same for'a short time. When this point of time has been passed the temperature rises again uniformly. I have given that temporary interruption, in the time-temperature-curve (curve of state) the designation bending place. It may be that when the supply ofheat is continued and the temperature again rises another bending place appears which then proves that the molten metal is not actually a metal but a metal-compound. I'have found that the reactivity of the oxide compounds present in the zinc is so high within said temperature range they can be reduced by being brought into contact with certain solid metals without the latter alloying with the zinc.

Referring now to the annexed sheet of drawings on which is shown a diagram, or a timetemperature-cur've, I beg to state what follows: I have discovered the fact, that,, as regards virgin zinc obtained from the smelting of zinc ores, two bending places arise, and with respect thereto I refer to the above-mentioned figure, from which appears that when thezinc is heated from zero up to 419 C. a straight, obliquely upwardly directed line C is obtained, but at 419 the line extends horizontally, forming now the short line C indicating a certain period of time in which the melting of the zinc has further proceeded. Then, on continuing the supply of heat, another oblique line C is formed until the temperature has risento 428 or more, viz. up

to 441 (short horizontal line C), according to the quality of the zinc ore. After 441 appears again an upwardly directed oblique portion of the original line C. The portions C and C constitute the above-mentioned bending places. The second thereof lies considerably remote from the first which constitutes the generally known fus g point of the zinc which is 419 c. That difference cannot be due, according to my opinion, to the generally known inclusions in virgin zinc obtained by the smelting of zinc-ores, or in technically pure zinc, viz., for instance, iron, cadmium, etc., the proof residing in the fact that when I removed from the molten zinc by known means the iron etc. this did not change in the least the position of said bending places. I have investigated the matter repeatedly, always with tracing the curve on co-ordinate system, but always with the same result. It is, therefore probable or at least'possible that a ternary system is the cause of the irregularity of the curve.

That solid iron diffuses in zinc even at a temperature lying by far below its fusing point; in other Words, that liquid zinc is able to melt even considerable amounts of iron with, in fact, considerable speed, forming hard zinc, is generally known, and it is likewise a known fact that the walls of the iron melting vessels are very quickly destroyed by the liquid zinc contained in said vessels. This known formation of hard zinc is an example of the strong tendency of molten zinc and solid iron to diffuse, but nevertheless I have determined that, if certain rules are observed, other metals, also metal salts, do not combine with technically pure zinc, but owing to their greater tendency to diffuse with the oxygen compounds contained in said zinc combine with these oxygen compounds instead of with the zinc.

That is the case, for instance, if aluminium or copperor magnesium is added to the molten zinc in the manner disclosed in the present invention, that is to say, under conditions on which depend the great diffusing tendency between the molten technically pure zinc and the added metals, other than iron, or metal salts.

If,-thus, for instance, solid metallic aluminium is added to the molten zinc at a temperature lying between the two bending places of the curve of state and if at the same time the zinc and the added substance are mechanically moved with respect to one another, the aluminium does not combine with the 'zinc, forming an alloy therewith, but combines with the oxygen contained' in the zinc, i. e. with the oxygen-component of the same. The zinc is, thus, deprived of the oxygen, but as the compound formed by the added metal and the oxidic inclusions of the zinc have a lower specific weight than an alloy of the zinc and the added metal, the compounds formed by the added metal and' the oxidic inclusions of the zinc rise and appear on the suraraaaoc face oi the molten mass where it can be easily removed.

If the zinc and the added substance, say alumi-' nium, are not mechanically moved with respect ,to one another while that substance is being added, this latter will not come sumciently in contact with the molten zinc, i. e. with the oxidic component of the same. The aluminium etc.

will, of course, exert their influence also upon the oxidized inclusion with which they come in contact, if the mechanical movement of the substances relatively to another is omitted, but when that action has been finished, the adjacent-oxidized inclusions will not likewise be actedon, but

interval, which is one of the characteristic features of the invention, the second characteristic feature being the movement of the substances relatively to one another whereon depends the complete success of the method.

I am aware of the factthat aluminium is already used as deoxidation agent in the manufacture of which it is used are, in that case, quite other ones'than in the present case, especially as the aluminium is employed as a liquid deoxidation agent to act on liquid steel. In the present invention the aluminium is preferably employed in solid state wherein lies an essential difierence leading to a considerable improvement andv progress.

I am, further, aware of the fact that zincaluminium alloys having a large percentage of aluminium have already been added to liquid zinc, the object being however, not to bring about a deoxidation of the molten zinc, but the reasons are quite other ones, and: there is no account of adding the. zinc-aluminium alloy at a certain distinct interval of time, on the temperature curve, nor of moving the zinc and the added alloy mechanically with respect to one another.

In carrying out the process according to the invention care is to be taken that the de-oxidi'zing metal which is introduced into the molten zinc is in such an exterior form that it can enter into contact with the fused mass as intimately and extensively as possible. Conse; quently arrangements must be used which help to promote this object. Such means consist in the exertion of a relative motion between the melt and the de-oxidizing metal, which can be carried out without perceptible resistance, andsuch a motion can with advantage be efiected with intimate and extensive contactif the deoxidizing metal is in the form of plates provided steel. But the presuppositions under interval while with a plurality of openings, such as is the case for example with nets, lattices, perforated sheets, gauzes, wire fabrics and the like. Such forms for the tie-oxidizing metal consequently do not need to be chosen so thick that they hinder the ease and rapidity of the motion and the flow of the fused mass through thesame.

The most striking and greatest advantage which the invention presents consists therein that the tendency of the oxidized zinc to take up again, in liquid and in solid state, fresh oxygen from the air is greatly reduced.

Another important advantage is the reduction of the diflusion-tendency and the diffusion speed when the vzinc treated according to this invention comes into contact with other metals for in stance with iron or lead. This is particularly advantageous when alloys are to be made.

I claim:

1. Aprocess for pure zinc as produced in zinc smelting works and containing besides small quantities of iron also oxygen compounds, consisting in this that the zinc, during the heating of the same within the temperature interval between a lower point and an upper point ascertainable from the time-temperature curve, which points are determined by the fact that the zinc in spite of uninterrupted heat supply shows no heat increase for a time, is brought with exertion of a relative motion into intimate and extended contact with a metal having agreat tendency to absorb oxygen and melting at a higher temperature than zinc.

2. A process for the deoxidation of technically pure zinc as produced in zinc smelting works and containing besides small quantities of iron also the deoxidation of technically oxygen compounds, consisting in this that the of the same within the point and an upper point ascertainable from the time-temperature curve, which points are determined by the fact that the zinc in spite of uninterrupted heat supply shows no heat increase for a time, is brought with exertion of a relative motion into intimate and extended contact with aluminium of a form such that the zinc is compelled during the motion to flow through numerous openings arranged in the aluminium.

3. A process as claimed in claim 2 in which the aluminium consists of a plate having numerous flow-through openings.

4. A process for the deoxidation of technically pure zinc as'produced which has a low iron content and also oxygen compounds which comprises heating said zinc to the interval shown by the tune-temperature curve of the zinc, as lying between the point of beginning fusion and that of beginning solidification oi the zinc, and maintaining it at this bringing it into intimate and extended contact with aluminum by relative movement between the zinc and said aluminum.

- FRANZ SCHREBER.

by zinc smelting works 

